The invention relates to a device and a method for heated tool welding.
Heated tool welding is often used for fixing welding parts to a body. Heated tool welding methods are particularly used when the body and welding part are made from thermoplastic materials. One field of application for such heated tool welding more particularly arises if the welding parts are welded to a blown article as the body. Such blown articles are e.g. fuel tanks of motor vehicles, to which are fixed numerous welding parts, e.g. tank filling pipes, connecting lines, etc. using heated tool welding.
For this purpose normally use is made of welding machines, which have a force-controlled infeed drive and which are able to move a welding head with a gripper for the welding part on the one hand to the transfer point for the welding part and on the other to a fixed welding point. For each welding part it is necessary to provide a separate infeeder, which is only able to weld the welding part at a predetermined point. In order to attain a reliable, fluid-tight welding process, the heated tool welding must take place in force-controlled manner with respect to the application force both of the heating mirrors and the welding part to the welding point.
The problem of the invention is to develop a device and a method for heated tool welding able to fit by heated tool welding fittings to different points of a body.
According to the invention this problem is solved by the device and method according to the independent claims 1 and 7.
A device according to the invention for heated tool welding has a welding head, which is fixed to an infeed drive for moving the welding head. According to the invention the infeed drive is an industrial robot. The welding head is positioned by the industrial robot in coordinate-controlled manner into a clearly defined changeover position with respect to the welding point on the body and in force-controlled manner from the changeover point to the welding point.
A heated tool welding device constructed in this way has the advantage that through the industrial robot in its movement area it permits virtually random orientations between the body and the welding part. Thus, it is possible to move the welding head to different points with respect to the body. By means of a single gripper on a single welding head it is consequently possible to fix several identical welding parts to a single body. Simple resetting to different bodies is also possible, because for this purpose it is merely necessary to preset different coordinate values for the changeover point and for the infeed direction of the welding head from the changeover point to the welding point.
The industrial robot is preferably a 6-axis industrial robot. Such industrial robots have the greatest freedom of movement for the final effector fixed thereto, in this case the welding head.
A preferred development of the invention provides a force sensor for determining the forces in all directions between the robot arm and welding head.
According to another preferred development of the invention the welding head can be automatically coupled to the robot arm. This makes it possible with a single industrial robot to automatically change the welding head and consequently provide a single body with different welding parts, which need not necessarily be weldable with the same gripper and the same heating mirrors for the body and the welding part. Besides one changer for the entire welding head, it is also possible to provide a changer for the gripper of the welding part. This is advantageous if the welding parts admittedly have such similar welding points that a heating of both the welding point and the welding part can take place by means of the same welding mirror, but the shape of the welding part makes it necessary to use different grippers for the welding parts. As a result of this construction it is possible to equip a single body with all the welding parts to be fitted thereto. As a result of the short setting up times it is possible to very flexibly adapt to the body. As a result of the very free determination of the position of the welding points, it is also possible to equip bodies having the most varied shapes with the same device with the welding points thereof. This makes it possible with short setting up times and low setting up costs to equip small batches on the same welding device for heated tool welding.
According to another preferred development of the invention the difference between the force between welding head and robot arm at the changeover point compared with the actual values is used as a reference quantity for the force control.
According to an inventive method the welding head is firstly moved to an acceptance point, where a welding head-side gripper accepts a welding part. The welding head is then displaced and oriented in coordinate-controlled manner in a changeover position preset on the body with respect to the welding point of the welding part to be welded. Subsequently there is a change from coordinate control to force control. The welding head is moved on a predetermined path in force-regulated manner to the welding point.
According to a preferred development, the forces acting between the welding head and robot arm are measured for force regulation purposes.
According to another preferred development the forces measured in the changeover position between robot arm and welding head are used as the reference quantity for force regulation.
According to an advantageous development the desired forces for the force regulation are preset as a function of the welding process.
According to another preferred development the force components of the desired force are preset in such a way that the desired force is oriented perpendicular to the body surface at the welding point.
It is also advantageous for the method to be such that initially a heating mirror passes with a predetermined pressing force into engagement with the welding point of the body. The welding head is then moved into an intermediate position, where the welding head is no longer in contact with the body. In the intermediate position the welding part is oriented towards the welding point and is subsequently brought in controlled manner into engagement with the body.
According to a preferred development of the invention the intermediate position corresponds to the changeover position. It is also advantageous to perform the orientation of the welding part towards the welding point without any movement of the robot arms in the robot head.